The present invention relates to a direct heat-sensitive lithographic printing plate precursor for offset printing which requires no development and is excellent in press life, a negative type non-processing lithographic printing plate precursor and a method for producing the same, and a method for lithographic printing using the same. More specifically, the present invention relates to a lithographic printing plate precursor or a negative type non-processing lithographic printing plate precursor and a method for producing the same which can be produced by heat mode image recording, is capable of image-recording by scanning exposure based on digital signals, can be developed with water, or is loadable on a printer without development and printing can be performed as it is, and a method for lithographic printing.
A lithographic printing plate generally comprises a lipophilic image area which receives an ink during printing and a hydrophilic non-image area which receives fountain solution. As such a lithographic printing plate precursor, a PS plate (presensitized plate) comprising a hydrophilic support having provided thereon a lipophilic photosensitive resin layer has so far been widely used. A plate-making method of a lithographic printing plate precursor generally comprises performing exposure through the image of a developed lith film and the like and then dissolving and removing a non-image area with a developing solution to thereby obtain a printing plate.
The conventional plate-making process of a PS plate is accompanied by the wet operation of dissolution and removal of a non-image area after exposure, and it has been desired to cease to use or simplify such a wet process. In particular in recent years, since the disposal of waste solutions which are discharged as a result of the wet process not only imposes economical load on the industry but also has become a great concern in the industry at large from the standpoint of global environmental protection, there is an increased demand for the improvement in this aspect.
As one simple plate-making method which meets the above demand, there has been suggested a method of using an image-recording layer by which the removal of the non-image area of a printing plate precursor can be performed in usual printing process, and effecting development after exposure on a printer, to thereby obtain a final printing plate. A system of plate-making of a lithographic printing plate by such a method is called an on-press developing system. Specifically, for example, a method of using an image-recording layer soluble in a fountain solution and an ink solvent, and a method of conducting mechanical removal of a non-image area by contact with the impression drum and the blanket drum in a printer can be exemplified. However, a big problem of the on-press developing system is that complicated means should be taken such that a printing plate precursor must be stored under a completely light-shielded state or under a constant temperature condition during the period of time until the printing plate is loaded on a printer because an image-recording layer is not fixed after exposure.
On the other hand, as another trend in this field, digitized techniques of electronically processing, accumulating and outputting image data using a computer have prevailed, and various image output systems corresponding to these digitized techniques have been put to practical use. As one example of such techniques, a computer-to-plate technique directly making a printing plate is attracting public attention, which comprises scanning exposing a printing plate precursor with high convergent radiant rays such as laser beams carrying digitized image data without using a lith film. With such a tendency, it has become an important technical subject to obtain the printing plate precursor well adapted to this purpose.
Accordingly, the simplification of plate-making and the realization of dry system and non-processing system have been further strongly desired from both aspects of the above-described environmental protection and the adaptation for digitization.
Solid state lasers having high output, e.g., a semiconductor laser and a YAG laser are inexpensively available in recent years. As a result, as a producing method of a printing plate by scanning exposure which is easy to be incorporated in a digitized technique, a plate-making method using these lasers as an image-recording means is promising. In conventional plate-making methods, image-recording is performed by imagewise exposing a photosensitive printing plate precursor in low to middle degree to cause the change of physical properties of the image on the surface of the precursor by a photochemical reaction. On the other hand, in a method of using the exposure of high power density by a high output laser, a large quantity of light energy is irradiated on an exposure region convergently during a momentary exposure time, the light energy is efficiently converted to heat energy to cause a chemical change, a phase change, or a thermal change such as the change and rupture of form and structure due to the heat, and that change is utilized in image-recording. That is, image data are inputted by light energy such as laser light, but image-recording is performed by the reaction due to heat energy. This recording system making use of heat generation by high power density exposure is generally called heat mode recording and converting light energy to heat energy is called light/heat conversion.
A big advantage of a plate-making method utilizing a heat mode recording means is that a material is not sensitive to light of general illuminance level, such as room illumination, and images recorded by high illuminance exposure do not necessitate fixation. That is, when a heat mode material is used in image-recording, the material is safe to room light before exposure and fixation of the image after exposure is not essential. Accordingly, for example, when an image-recording layer which is insolubilized or solubilized by heat mode exposure is used in a plate-making process of imagewise removing an exposed image-recording layer to make a printing plate by the on-press developing system, it becomes possible to realize a printing system in which an image is not influenced even when the development (the removal of a non-image area) is exposed to atmospheric light in a room for a certain period of time after image exposure.
Accordingly, if heat mode recording is utilized, it is expected that it will be possible to obtain a lithographic printing plate precursor which is adapted to the on-press developing system, in particular, easily developed to a computer-to-plate system.
As one means of heat mode system which has been advanced as a measure against the simplification of plate-making process, a technique of microencapsulation has been considered.
Plate materials comprising a support having provided thereon a heat-sensitive recording layer comprising a microencapsulated heat-melting substance and a binder resin, wherein a heated part is converted to a lipophilic part, are disclosed in JP-A-3-108588 and JP-A-5-8575 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). However, since any of the microencapsulated heat-melting substances disclosed in these patents does not have reactivity with the medium, the diffusibility is large and satisfactory discrimination cannot be obtained. On the other hand, lithographic printing plate precursors comprising a support having a hydrophilic surface having provided thereon a recording layer containing an active hydrogen-containing binder polymer together with block isocyanate, and methods for producing the same are disclosed in JP-A-62-164596 and JP-A-62-164049. However, these printing plate materials necessitate the development process to remove a non-printing part after printing.
Further, as one direct type lithographic printing plate material, there is a direct drawing type lithographic printing plate material, wherein an image area is formed on the surface of a hydrophilic layer by external means such as ink jet and toner transfer, and a trial to incorporate a microencapsulation technique to these techniques has been performed. A printing plate material comprising coating a microencapsulated non-reactive heat-melting substance and forming a toner-receiving layer by heat printing is disclosed in JP-A-62-1587. However, this material becomes a printing plate for the first time when a lipophilic toner, etc., are fixed on the formed toner-receiving layer and not an image area is formed after printing.
JP-A-7-1849 discloses a technique which contrives to improve the press life of a printing plate by adopting the mechanism that a lipophilic component in a capsule and a hydrophilic binder polymer bring about chemical bond at the interface between a microcapsule and a binder to thereby suppress swelling. This printing plate precursor certainly meets the demand of the market but since the technique is a system of causing heat rupture of the capsule by means of a thermal head, and then forming an ink-receiving area by the reaction of the lipophilic substance with the binder, enlarging of a hydrophobic area due to the diffusion of the lipophilic substance is expected, therefore, not suitable for highly precise imaging.
As has been described above, even when a technique of microencapsulation was employed, various drawbacks as to conventional materials for a heat-sensitive lithographic printing plate such that press life, discriminability and lipophilicity were unsatisfactory have not been dissolved, therefore, the use has been limited to light scale printing.
As one preferred plate-making method of lithographic printing plate based on heat mode recording, a method has been suggested which comprises providing a hydrophobic image-recording layer on a hydrophilic substrate, imagewise exposing the hydrophobic layer by heat mode exposure to change the solubility and dispersibility of the hydrophobic layer, and, if necessary, removing the non-image area by wet development.
As an example of such a printing plate precursor, there is disclosed in JP-B-46-27919 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) a method for obtaining a printing plate by heat mode recording a plate precursor comprising a hydrophilic support having provided thereon a recording layer showing a so-called positive function, i.e., whose solubility is improved by heat, specifically a recording layer having a specific composition such as saccharides and melamine-formaldehyde resins. Since disclosed simple plate-making techniques of heat mode recording including the above method are generally not sufficient in heat sensitivity, sensitivity is extremely insufficient for heat mode scanning exposure. Accordingly, the discrimination of hydrophobicity/hydrophilicity of the irradiated part and the non-irradiated part, i.e., the discrimination of an image area and a non-image area, is small, which has been the restriction in practical use. When the discrimination is insufficient, plate-making according to the on-press developing system is substantially difficult.
As the means to solve that problem, methods to remove the image layer at the irradiated part by heat splashing due to the work of heat by high output laser beam irradiation (called abrasion) are disclosed, e.g., in WO 98/40212, WO 98/34796 and JP-A-6-199064, specifically lithographic printing plate precursors capable of plate-making without performing development which comprise a hydrophilic layer containing transition metallic oxide colloid as the upper layer and a lipophilic image-recording layer as the lower layer are disclosed. The discriminability of the irradiated part and the non-irradiated part where heat splashing has been completely performed is certainly large according to these methods, but there are other problems that the printer is stained by the splashed matter, the stain on the printing plate surface impairs the operation of the printer and printing quality, in addition, the heat of the irradiated light often does not reach the deep part of the image-recording layer, as a result, the bottom part of the image-recording layer near the support is not splashed and remains, i.e., the phenomenon called a residual film is brought about. The substantial discriminability cannot be exhibited due to the residual film, which leads to the reduction of printing quality.
As is the situation, as a method not accompanied by such drawbacks, there are disclosed simple plate-making methods making use of the change of the degree of hydrophilicity/hydrophobicity of the surface by heat, i.e., the change of polarity, not according to abrasion even when an image is formed by heat mode light irradiation. For example, methods comprising adding a thermoplastic polymer such as hydrophobic wax and polymer latex to a hydrophilic layer and hydrophobitizing by phase separation to the surface by heat are disclosed in JP-A-58-199153 and U.S. Pat. No. 3,168,864. These techniques suggest a direction of the improving means of discriminability. However, since these disclosed techniques are insufficient in discriminability and there is apprehension about smearing (i.e., staining) of printed matter due to, in particular, insufficient hydrophilicity, the improvement is desired.
Sufficient discrimination of an image area and a non-image area is a fundamental important characteristic directly linked with the improvement of printing quality and press life, hence the development of a plate-making method having discriminating property and easiness of print-making operation, in particular, a method having high discriminating property, high sensitivity, necessitating no development process and capable of heat mode plate-making is desired.
Heat hydrophobitization by heat mode recording has been tried. For example, printing plate materials comprising a support having provided thereon a heat-sensitive layer are disclosed in JP-A-53-64747 and JP-A-1-113290, wherein plate-making is performed by heat printing and melting a heat-melting resin and a thermoplastic resin dispersed in the heat-sensitive layer, and the heated part is converted from hydrophilic to lipophilic, and U.S. Pat. Nos. 4,034,183 and 4,063,949 disclose printing plate materials (i.e., precursors), wherein a hydrophilic polymer provided on a support is irradiated with laser beams to dismiss hydrophilicity and convert to hydrophobicity (i.e., lipophilicity). However, these materials have a drawback that a non-image area is smeared (i.e., stained) since the heat-melting substance on the plate surface is ink-receptive, therefore, the discrimination of an image area and a non-image area is low.
On the other hand, a lithographic printing plate precursor comprising a support having provided thereon a hydrophilic crosslinking layer and a lipophilic light/heat conversion layer, which requires no development for plate-making, is disclosed in EP 94/18005. However, the plate-making necessitates the operation of taking the crosslinked hydrophilic layer away, therefore, it is thought that there is a problem in the point of simplicity.
Further, a lithographic printing plate precursor comprising a support having provided thereon a hydrophilic layer containing metallic oxide colloid and a lipophilic image-recording layer containing a light/heat conversion substance and requiring no development for plate-making is disclosed in WO 98/40212. However, at least the present inventors have thought that there are many problems to be solved to secure the discriminability of an image area and a non-image part when a light/heat conversion layer is lipophilic.
A lithographic printing plate precursor comprising a support having provided thereon a hydrophilic image-recording layer containing a light convertible and ink-receptive light-absorbing substance, e.g., a dye and a pigment, and a colloidal dispersion of metal or metallic oxide and requiring no development for plate-making is disclosed in WO 99/04974, but as the examples of the specific light/heat converting agent, there are merely disclosed two kinds of light-absorbing cationic dyes and carbon black.
Lithographic printing plate precursors by laser beam recording are disclosed in JP-A-6-199064 and WO 98/40212, which comprise two-layer constitution using in combination of a layer containing a light/heat converting agent and a layer differing in the degree of hydrophilicity/hydrophobicity from the above layer. These techniques suggest the way to advance further improvement.
Further, as another big problem in conventional heat mode positive system printing plate precursors, there is the phenomenon called a residual film in a non-image area. That is, the defect that the change in solubility in a recording layer by exposure is small in the vicinity of a support as compared with that in the vicinity of the surface of a recording layer to leave a film substance which is not dissolved and removed is liable to occur and the improvement of this point has been required. In general, in a heat mode positive type printing plate precursor, the heat generation by heat mode exposure is based on the light absorption of the light absorbing substance in a recording layer, hence the generated amount of heat is liable to be large on the surface of a recording layer and small in the vicinity of a support. Therefore, the degree of hydrophilization of a recording layer in the vicinity of a support relatively decreases. As a result, a hydrophobic film is often not removed completely and remains as it is at an exposed part which is substantially to provide a hydrophilic surface. Such a residual film on a non-image area generates smearing on prints. Conventionally used separate function type multilayer structures comprising a light/heat conversion layer and an image-recording layer are disadvantageous in this point.
As is shown in the above-described details of the plate-making/printing technique according to heat mode image-recording, the characteristic advantage of this plate-making/printing technique is that a printing plate can be made directly from a block copy requiring no film, hence on-press plate-making without developing operation is possible. On the other hand, this technique has drawbacks that heat mode sensitivity is insufficient, an image-forming substance is diffused by heat, and the sensitivity is different at a surface area and a bottom area of the image recording layer. These drawbacks are the defects which fundamentally bring about the deficiency of the discriminating property of an image area and a non-image part, hence these are also the defects which directly lead to printing quality and press life. Accordingly, a fundamental means to improve both printing quality and press life of a plate-making/printing method utilizing heat mode image-recording is exclusively to improve the discriminating property. It is expected that the solution of the discriminating property naturally leads to the solution of the above-described other various defects.
An object of the present invention is to provide, by solving the above defects of heat mode plate-making methods using laser beams, etc., a heat mode type lithographic printing plate precursor capable of plate-making after short time scanning exposure without performing development process, excellent in press life, and generating no smearing (i.e., no staining) on a printing plate surface.
Another object of the present invention is to provide a heat mode type lithographic printing plate precursor which is excellent in the discriminating property of an image area and a non-image area, from the viewpoint of the specific means for improving both press life and the prevention of printing smearing.
A further objects of the present invention are to solve the above-described defects of heat mode plate-making systems and improve printing performance, i.e., to provide a heat mode type (negative) lithographic printing plate precursor capable of easily plate-making, capable of being loaded directly on a printer and plate-making, excellent in press life, and hardly generating smearing on a printing plate surface, to provide a method for producing the same, and to provide a method of lithographic printing using the same.
In particular, an object of the present invention is to provide a heat mode type lithographic printing plate precursor capable of easily plate-making according to scanning type image exposure by a laser beam and excellent in discriminating property of an image area and a non-image area.
The present inventors thought that the key to the solution of the above problems is to find a novel means to give the maximum change from hydrophilicity to hydrophobicity by imagewise light irradiation. As a result of earnest investigation, the present inventors have found the new principle of revealing discriminating property, and the present invention has been attained based on the principle.
In addition, concerning the above objects, the present inventors paid attention to conspicuous ink receptivity (hydrophobicity) and mechanical strength (press life) of a continuous phase metal surface, and as a result of the eager search for the means of imagewise distributing a metal layer on a hydrophilic surface, the present inventors obtained the idea of forming a metal-fused layer by heat and repeated examinations, thus the present invention has been achieved.
That is, the embodiments and the preferred embodiments of the present invention are as follows.
(1) A lithographic printing plate precursor which comprises a support having provided thereon a layer comprising a hydrophilic medium, wherein the layer comprising a hydrophilic medium contains a hydrophobitization precursor having a hydrophilic surface and a light/heat converting agent which is hydrophilic in itself, or at least on the surface.
(2) The lithographic printing plate precursor as described in the above item (1), wherein the layer comprising a hydrophilic medium is sol/gel convertible.
(3) The lithographic printing plate precursor as described in the above item (1) or (2), wherein the hydrophobitization precursor having a hydrophilic surface is a particle dispersion of composite constitution containing a hydrophobic substance at the core part and having a surface layer of superficial hydrophilicity.
(4) The lithographic printing plate precursor as described in the above item (1), (2) or (3), wherein the light/heat converting agent is a solid fine particle selected from the group consisting of a metal, a metallic compound, a pigment and a carbon simple substance each having a hydrophilic surface, or a hydrophilic dye which is soluble in a hydrophilic medium.
(5) The lithographic printing plate precursor as described in the above item (1), (2), (3) or (4), wherein the printing plate precursor is provided with a water-soluble protective layer.
(6) A method of lithographic printing which comprises imagewise irradiating the lithographic printing plate precursor described in any of the above items (1) to (5) with light/heat convertible visible rays or infrared rays, bringing the irradiated part into contact with an ink to make the image area accept the ink to form a printing plate surface, and performing printing.
The embodiments and the preferred embodiments of the present invention are further described below.
(7) A lithographic printing plate precursor, which comprises a hydrophobic area imagewise formed by imagewise irradiating the printing plate precursor containing particles having hydrophilic surfaces carrying a metallic fine piece (sometimes, called a metallic dust) by heat mode exposure of light and thermo-fusing the metallic fine piece on the irradiated part.
(8) The lithographic printing plate precursor as described in the above item (7), wherein the particles having hydrophilic surfaces carrying a metallic fine piece are the surfaces of a metallic compound having photocatalytic property.
(9) The lithographic printing plate precursor as described in the above item (7), wherein the particles having hydrophilic surfaces carrying a metallic fine piece are the surfaces of a metallic compound sparingly soluble in water.
(10) A method for producing a lithographic printing plate precursor which comprises performing imagewise irradiation of heat mode light exposure on the printing plate precursor containing superficially hydrophilic particles carrying a metallic fine piece, and thermo-fusing the metallic fine piece on the irradiated part to thereby form an imagewise ink-receptive hydrophobic area.
(11) A method of lithographic printing which comprises performing imagewise irradiation of heat mode light exposure on the printing plate precursor containing superficially hydrophilic particles carrying a metallic fine piece on the surfaces, and thermo-fusing the metallic fine piece on the irradiated part to form a hydrophobic area of an imagewise metal thin layer, thus the imagewise hydrophobic area forms an ink-receptive printing surface.
The fundamental of the present invention is the discovery of the principle that the surface of a printing plate precursor should be sufficiently hydrophilic for exhibiting the discriminating effect of an image area and a non-image area after plate-making to the best of the ability, which contributes to increase the difference between the hydrophobicity and hydrophilicity of an irradiated part and a non-irradiated part, and insufficient hydrophilicity of the surface of a printing plate precursor cannot be compensated for by the reinforcement of the hydrophobicity in an irradiated part. Based on the principle, the present invention makes it a fundamental constitution that all of the constitutional elements of an image-recording layer provided on a support, i.e., the medium of an image-recording layer, the surface of a hydrophobitization precursor, and a light/heat converting agent itself, or the surfaces of a light/heat converting agent when it takes the form of particles are hydrophilic. When the image-recording layer of such constitution is imagewise irradiated, the light/heat converting agent generates heat, the hydrophobitization precursor makes the vicinities hydrophobic by the heat, and the hydrophobicity of the image area formed exhibits apparent discriminability between the hydrophilicity of the non-image area, which becomes the key to increasing the ink-repellency of the non-image area to prevent printing smearing and improving the press life when a printing plate is formed.
In the present invention, it is devised to hydrophilize each constitutional element of the image-recording layer to meet the fundamental.
In the first place, with respect to the medium, highly hydrophilic media are sol/gel convertible media, in particular, sol/gel convertible media which are converted from metallic oxide sol to metallic oxide gel structure by dehydration condensation represented by sol/gel conversion system of silanol/siloxane described later are preferred.
To further improve the hydrophilicity of the image-recording layer, it is effective to incorporate colloidal dispersion selected from the group consisting of highly hydrophilic silica, silicon hydroxide, aluminum hydroxide, aluminum oxide, titanium oxide and titanium hydroxide into sol/gel convertible hydrophilic media.
In the next place, hydrophobitization precursors having hydrophilic surfaces are (1) a precursor which is a dispersion of particles of composite constitution containing a hydrophobic substance at the core part and having a surface layer of superficial hydrophilicity, and the incorporated hydrophobic substance makes the vicinities hydrophobic due to the work of heat by light irradiation and light/heat conversion, and (2) a precursor which is a dispersion of particles having hydrophilic surface and heat-crosslinkable and exhibits hydrophobicity by the initiation of a crosslinking reaction due to the work of heat.
As the preferred forms of the former dispersion of particles of composite constitution, the following can be exemplified:
(1) So-called hetero coagulation particles containing a thermoplastic resin which softens or melts by the temperature of heat mode image exposure and hydrophilic sol particle layers coagulated and adhered on the surfaces,
(2) Hydrophilization treated particles containing a thermoplastic resin which softens or melts by the temperature of heat mode image exposure and hydrophilic surface layers such as sol/gel conversion layers are formed on the surfaces,
(3) Core/shell type composite particles comprising hydrophobic fine particles of a thermoplastic polymer obtained by dispersion polymerization as the core part and hydrophilic polymer layers formed around there,
(4) Emulsified particles of a thermo-diffusible or thermoplastic hydrophobic organic compound emulsified and dispersed in a hydrophilic medium, and
(5) Microencapsulated particles comprising a hydrophobic core substance protected with a wall material having hydrophilic surface.
These particles will be described in detail in the following detailed description of the invention and in the examples.
As the latter particle dispersions which exhibit hydrophobicity by the initiation of a crosslinking reaction by heat, mixed dispersions of a polymerizable monomer and a crosslinkable compound can be exemplified.
In addition, compounds and groups of compounds having the function of hydrophobitizing the vicinities of the particles by the work of heat can be used as the hydrophobitization precursors in the present invention.
Specific hydrophobic compounds which can be incorporated into the emulsified and dispersed particles (4) or in the microencapsulated particles (5) are liquid or solid organic low molecular compounds having the melting point of 300xc2x0 C. or less and the boiling point of 100xc2x0 C. or more at normal pressure, and organic high molecular compounds having a solubility in 100 g of water at 25xc2x0 C. or the amount of water absorption per 100 g of water at 25xc2x0 C. of 2 g or less.
The organic low molecular compounds particularly preferably have the above-described melting point and boiling point and, in addition, at least either (1) the solubility in 100 g of water at 25xc2x0 C. is 2 g or less, or (2) the ratio of organic property/inorganic property in the organic conceptual drawing is 0.7 or more.
On the other hand, organic high molecular compounds which can be incorporated into these particles are preferably at least one of polyurethanes, polycarbonates, polyesters, polyacrylates, cellulose esters, and cellulose acetals.
In the next place, light/heat converting agents contained in a hydrophilic medium are light/heat convertible solid fine particles whose surfaces are hydrophilized, or light/heat convertible and biodegradable hydrophilic dyes capable of being dyed or molecularly dispersed in a medium. The solid fine particles are selected from the group consisting of metals, metallic compounds, pigments and carbon simple substance.
It is preferred for the surface of the printing plate precursor according to the present invention to be provided with a water-soluble protective layer for preventing smearing (i.e., staining) of the printing plate precursor during handling, in particular, for preventing hydrophobitization.
The present invention summarized above will be described in further detail below.